The effects of cage aquaculture on freshwater ecosystems are determined by multiple farming and environmental variables, and thus, the assessment of a wide range of abiotic and biotic variables enables better understanding of the impacts generated by this nutrient source. This study was carried out at Castanhão reservoir located in the State of Ceará, which is the largest Brazilian producer of Nile tilapia in cage systems, wherein about 8000 reservoirs provide a vast area to expand not only this important socio-economic but also pollution-prone activity. Nutrient mass budget, water quality monitoring, hydrodynamic characterization, and elemental/stable isotopic composition of end-member products were measured in cage aquaculture and other reservoir areas in order to determine the relative effects on reservoir conditions. Nutrient budgets showed that 34% of the artificial feed was lost to the water column but water quality monitoring and isotopic composition analysis suggested that the cages were not extensively impacting the water quality probably because of the physiographic and hydrodynamic features of the cage site.
Worldwide, the marine debris emissions have been provoking impacts in ecosystems, generating massive mortality of different species with commercial interest. In South America, we have a lack of studies to verify the marine debris composition in transitional environments such as adjacent regions of coastal jetties. These are hydraulic engineering constructions used to maintain the navigation channel access between the sea-estuarine interface and are also used by teleost fishes, crustaceans, and mollusks like artificial shelters (reefs), being excellent fishing grounds. Therefore, the present study was devoted to qualitatively evaluate the composition of marine debris in an internal jetty portion of a Laguna Estuarine System (LES) located in South America (Brazil). Six hundred freediving were conducted to collect marine debris in the study region. The in situ campaigns were performed in 2016 during all spring season (sand substrata) in four distinct zones with 26,400 m each one covering almost all adjacent jetty extension, to evaluate possible spatial changes in the marine debris composition. All material obtained was identified, measured, weighed, and ordered in eight groups, with six groups being related to the fishing activity and two groups related to the tourism/community in the study region. So, it was possible to observe possible relations between the marine debris distribution to artisanal and recreational local fishing. After 600 freediving sampling efforts, 2142 marine debris items were obtained, totaling close to 100 kg of solid waste removed from the inner portion of the coastal jetty. Notably, 1752 units (50 kg) of fishing leads were collected being this item the main marine debris residue found in the four sampled areas, corresponding to nearly 50% of the total weight of the collected waste. Ninety-eight percent of marine debris were derived from the local fishing activities, and just 2% were derived from tourism/community. Considering the total contribution related to fishing, 83% of the marine debris were composed by lead (sinkers) adopted by recreational and artisanal fishing. Notably, the catch activity in this region has a close influence over the marine debris composition. Reductions of marine debris emissions derived from the fishing activities have been a global challenge, once this problem is occurring in practically all marine and estuarine environments under the anthropic action. The presence of marine debris changes the local landscape and can provoke serious environmental problems, such as ghost fishing that affects a wide variability of marine mammals, birds, and fishes. Most of marine debris collected came from recreational and artisanal fishing, being the fishing leads the most prominent material, especially in sector 4. This fact is possibly related to the intense mullet fishing using cast nets, usual in this sample area. In the other sectors, there was a great predominance of grapnel fishing leads, widely adopted by recreational fishermen in open water environments. The "fingernails"...
Domingos M.M., Dantas D.V. 2019. Proposed bycatch-reduction modifications of shrimp fyke nets used in South American lagoons. Acta Ichthyol. Piscat. 49 (1): 1-7.Background. Shrimp fisheries using fyke nets have been associated with a massive acquisition of teleost fishes as bycatch, potentially resulting in the decimation of their stocks. Based on this assumption, the presently reported study intended to test an alternative modification of a commonly used fyke net, in order to minimize the impact of its low selectivity. Materials and methods. To evaluate the alternative design proposed in this work, a total of 44 sampling efforts, including 22 with a control gear (CG) and 22 with a modified gear (MG), were conducted at a subtropical coastal lagoon system located in southern Brazil. In all trials, the fyke nets were installed at the fishing area approximately at 18:00 h and removed approximately at 06:00 h. The duration of each trial was nearly 12 h, which was similar to the catching time preferred by local fishermen. Results. Bycatch (BC) was preponderant in both modalities but the results showed that MG presented a reduction by 66 percentage points in BC catches, being more selective than CG. Additionally, the non-parametric test showed no significant differences of shrimp catches between the fishing gears used (MG and CG). So, the tested bycatch reduction devices (BRD) reduced the bony fishes acquisition preserving the volume of the target catch. Conclusion. The vertical opening reduction due the adoption of guiding panel + fan upper panel contributed to bycatch reduction, being a consistent BRD to reduce the potential impacts of this fishing gear over the bony fishes stocks.
We present an analysis of wind-sea and swell fields for mid-latitude and tropical Atlantic for the period 2002–2008 using a combination of satellite data (altimeter significant wave height and scatterometer surface winds) and model results (spectrum peak wave period and propagation direction). Results show a dominance of swell over wind-sea regimes throughout the year. A small but clear decrease in swell energy and an associated increase in wind-sea potential growth were observed in the NE trade winds zone. A seasonal summertime increase in wind-sea energy in the Amazon River mouth and adjacent shelf region and in African coast was apparent in the results, probably associated to a strengthening of the alongshore trade winds in these regions. Albeit with a significantly smaller energy contribution of wind-seas as compared to swell energy, we could say that a kind of mixed seas is more evident in the trade winds region, with the remaining area being highly dominated by swell energy. An analysis of wave-age shows the absence of young-seas. Only ~2% of all data points was classified as wind-sea, a classification confirmed by a fit to a theoretical relation between wind speed, peak period, and significant wave height for fully developed wind-seas.
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